Solar PV + waste heat 9

Comments View as Flat

1. 

   Earl Killian Posted 3:22 am
   01 Oct 2008

   This is not newPlease see http://www.omsolar.net/en/omsolar2/roof.html for a Japanese company's solution to the same problem that's been around for years.  The question is why it hasn't been done more?

   Permalink

2. 

   GreenEngineer Posted 7:39 am
   01 Oct 2008

   skepticalThis is an elegant idea, and one that I kicked around myself when I first started working in PV.  It's one of those things that is so obvious you have to wonder why it hasn't already been done on a wide basis.  My conclusion is that it is very hard to make it pencil out, for a few reasons:
   1) To effectively cool the panels on a hot day will probably require a liquid cooling loop.  Blowing ambient air (which will be pretty warm already in the summer) over the panels is unlikely to be effective.
   2)The temperature differential isn't that great.  The panels are probably in the ~120-150F range.  That's not a huge lot of delta T to work with.
   
   
   You have to have a place to dump the heat.  In the winter, this is easy, but I doubt the panels will get hot enough to benefit from the extra cooling under winter conditions.  During the summer, you're kind of stuck: You don't need home heating, and you don't have a coolth source to work with.
   The obvious idea, merging solar thermal hot water panels with solar PV, won't work unless you're solar hot water is on a flow-through basis (i.e. fresh water coming in all the time).  Solar hot water panels usually recirculate the working fluid in order to get it up to a useful temperature, but for this to work, the panel itself must be hotter than the fluid.  That's fine in the case of hot water panels.  But in the context of PV, that's the opposite of what you want.
   
   

   Permalink

3. 

   Biodiversivist Posted 9:15 am
   01 Oct 2008

   I share Dave's enthusiasm for combining solarand cogeneration but this is your typical newspaper article; vague, inaccurate.
   First, I suspect the president of the company (who immediately took his website down when he a reporter contacted him) may be deliberately misleading reporters to throw them off track ..."still making refinements, including the possible placement of stones beneath the panels". Riiight. Stones.
   "...no more than a quarter of the energy from the sun is converted to electric current."
   Today's mass produced commercially available photovoltaic panels don't convert a quarter of the light that hits them into electric current. Typical PV panels today convert about 10-14% of the energy that hits them into DC current under standard test conditions, with just a few panel designs claiming around 17%. Hot air will drop the efficiency, as will the inverters and so on until you are usually down to 7-9% of the sun's energy actually being put to use.
   "We make around 100 percent more energy than a regular PV system," he said.
   This statement could be true. You could double the 8% conversion of a typical PV panel to 16% by using, say, a heat pump coil under the panels to create hot water. Hopefully, this guy is really on to something and just doesn't want to let the cat out of the bag yet.
   Residential solar breaks down into two categories.
   
   
   New home construction
   
   Retrofit of existing homes
   
   
   Category 1 is restrained mostly by perceptions. People want to pour their money into cavernous homes that look "conventional" (something that gives them stature with their peers who are not Siberian reindeer herders who live in yurts). This limits how much will be invested in the solar and also its efficiency.
   Category 2 is held up by cost. You already have a mortgage on a McMansion that is mostly made of windows that does not have an unobscured south sloping roof and few are motivated to spend $6,000 to reduce their hot water bill 80% (which is just 20% of their total gas bill).
   
   In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

   Permalink

4. 

   GreenEngineer Posted 10:20 am
   01 Oct 2008

   heat pumpsThat's a good point, Biod.  That's the one way I can see to potentially get useful temperatures at the business end, without letting the panels themselves get particularly hot.  I'm not sure it would pencil out, since the heat pump uses electricity too -- it would depend on the specifics of the heat pump performance -- but it might.  Of course, you're now talking about a very significant cost add.  I can see it being financially feasible as part of an integrated house-wide thermal management system, that also included the AC system.  As a retrofit, though, I think it fails the giggle test (for money reasons, if not technical ones).

   Permalink

5. 

   Biodiversivist Posted 4:05 pm
   01 Oct 2008

   I suspect you're right GreenEI have to say, cogen combined with solar makes for some amazing efficiency gains. Cogen is probably going to be just as big as solar for residential (via heat exchangers and heat pumping).
   
   In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

   Permalink

6. 

   Pangolin Posted 7:56 pm
   01 Oct 2008

   Combine with geoexchange maybe? I keep seeing solar thermal panels as a natural adjunct to geoexchange systems. In northern climates the solar heat pumps the heat plume in the ground up during the summer and clear winter days. This allows for a smaller well system or lower pumping costs as the ground loop is warmer.
   In southern climates the PV panels collect power during the day and the geoexchange system pulls heat from both the panels and the house. The daytime coolant flow would move from the house past the solar panels and the heat pump feeds heat into the ground loop. When the sun goes down the flow can be reversed and the solar panels can now become pumped thermal radiators.
   The hottest coolant goes past the panels at maximum temperatures at night. By inserting the solar panels after the superheater into the night-time loop they radiate the maximum amount of excess heat at the night sky. If a certain amount of ground loop cooling happens this way power loads can be shifted from peak daytime load to cheaper night rates. Where wind power is available these cycles could switch on and off with the availability of electricity.
   It's just a wild hair on my part but I believe that some reduction in the size of each component of the total could be allowed by this kind of synergy. I've seen diagrams of solar-pumped geothermal heating and solar-pumped adsorption cooling so kludging the whole thing together shouldn't be impossible.
   
   Put the Carbon Back

   Permalink

7. 

   Biodiversivist Posted 1:21 am
   02 Oct 2008

   Lots of ideas out there PangolinEvery region requires a different design. No airconditioning here. I also envision switching coal power plants to smaller more dispersed gas fired that can come on line quickly to deal with variable solar and wind loads.
   
   In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

   Permalink

8. 

   amazingdrx Posted 3:08 am
   02 Oct 2008

   Solar cogenerationhttp://amazngdrx.blogharbor.com/blog/_archives/2005/6/19/ ...
   Yes!  With liquid cooling of concentraing solar collectors.  Mounted right on your roof.
   Heat hot water first, but what about extra summer heat?  Dump it into an underground loop under your building, it will store heat seasonally, insulate surface subsoil and vertically to make a seasonal storage heat sink.
   
   http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

   Permalink

9. 

   trock Posted 8:05 am
   02 Oct 2008

   Concentrated PVThat idea sounds like it to obvious to get it patented.  No doubt it was thought of by those who would use a design where the whole roof is used for heat.
   but what about combining concentrated PV's (CPV)with concentrated solar Power (CSP.)
   Run the same kind of CPV that they are now doing with CSP, but only in the beginning of the temperature loop.   That way your cooling water (liquid) of the PV's would be the first heated water (liquid) in a CSP.  I'm quessing that it would get to hot or inefficient at the hotter CSP tempertures.   (Asura's website says 560 C)
   I've read some CPV's are run at 1300 concentrations.  (I think these are still experimental, I really don't know.)  PV's cost a fair amount.   Mirrors cost some, but not as much as PV's.  What's the ratio of cost of mirror to PV?  What if I had a PV in my back yard and focused light on it at 100 concentrations?   Will it put out at 100 concentrations?   That's the heat I should be storing.
   Concentrated PV are not so good when a cloud comes by which is their downfall.   but how bad is it. Do I get no power?
   Okay, I quess my question is, has anybody done anything on CPV's in areas that are partly cloudy and how do they compare in cost and preformance?
   I mean it would be kind of nice to have one of those CSP designs that I would use as my CPV in my backyard (I've got a big backyard, I have a farm)
   
   Unless it costs to much.  I would build most of it myself.  
   (CPV makes some sense because it can be scaler, you could have a small one that might work.   CSP, no way, it has to be big for the efficiency to kick in)

   Permalink